(3) without the prior written consent of Lessor, install an Engine on an airframe leased to Lessee or in the possession of Lessee subject to a conditional sale agreement or owned by Lessee subject to a security agreement, provided, that: (A) such airframe is free and clear of all Liens except the rights of the parties to the lease or conditional sale or other security agreement covering such airframe and except Liens of the type permitted by clauses (A) and (B) of Section 6(a)(i)(2), and except the lien of any mortgage which either by its terms does not apply to the Engine or which effectively provides that each Engine leased to Lessee hereby shall not become subject to the lien thereof or to any rights of any party thereunder other than Lessee (with respect to Lessee' rights expressly granted hereunder), notwithstanding the installation of such Engine on any airframe subject to the lien of such mortgage; and (B) there shall be in effect a written agreement of the lessor or owner or secured